Inhibitions of microbial fermentation by residual reductive lignin oil: Concerns on the bioconversion of reductive catalytic fractionated carbohydrate pulp

Reductive catalytic fractionation (RCF) is an emerging biomass valorization strategy with high atom economy, which primarily outputting extensively depolymerized reductive lignin oil and highly delignified pulp. In downstream processes, the polysaccharide rich pulp can be potentially transferred into various value-added biochemicals through fermentation. In this study, the negative influences of the residual lignin oil that remaining on the surface of the RCF pulp towards different industrial microbes (total 9 species, categorized into eukaryotes, Gram-negative, and Gram-positive strains) was investigated. Results indicated the reduced lignin fractions were the key inhibitors in the RCF lignin oil, whilst the polarities, molecular weight, and the substi-tution groups of lignin possessed significant impacts on the growth of strains. Meanwhile, the resistance to RCF lignin oil by different category of industrial strains was analyzed. Generally, eukaryotes exhibited better resis-tance than the Gram-negative and Gram-positive strains. Took bioethanol and acetone-butanol-ethanol fermentation as examples, the negative influence of the lignin oil on biochemicals production using the RCF pulp as substrate was explored. Batch fermentation results revealed that the RCF lignin oil limited both the sugars (glucose and xylose) metabolism and the pathways toward bio-alcohols production of the microorganism. Therefore, it is vital to take continuous technical improvement in order to minimize the negative influences of the residual lignin oil on downstream biotransformation of the RCF pulps.

Automated summary

This study investigated the negative influences of residual lignin oil on the surface of RCF pulp towards different industrial microbes and analyzed the resistance of different categories of industrial strains to RCF lignin oil. Batch fermentation results revealed that RCF lignin oil limited the metabolism of sugars and the production pathways of bio-alcohols by microorganisms.